44 
the diameter in one direction that it possesses in another. By a mo- 
derate stroke against the side of one of these angular columns, one or 
more of them may be detached from the general mass. The sides 
of these columns will be found to be finely and closely striated lon- 
gitudinally, the strife being intersected by very fine and closely set 
transverse ridges. In those specimens in which the apices of the 
columns happen to be complete, they are concave, and have a pro- 
minent star, one-third of the diameter of the concavity, arising out of 
its centre. 
A careful examination of the beautiful web-formed star, which is ren- 
dered visible in every column, by a transverse polished section, as well as 
the striated plumose appearance which is manifested by a longitudinal 
section, shews the internal structure of the stone, and of course the 
curious fabric of the madrepore from which it derived its origin. 
Numerous and exceedingly slender longitudinal lamellfe correspond- 
ing with the external strife, are seen disposed perpendicularly from 
the circumference to the centre in a stellated form ; which are inter- 
sected by proportionally numerous and equally delicate lamellae, per- 
pendicularly disposed nearly in concentric circles: other lamellfe, 
answering to the external transverse ridges passing horizontally through 
both sets of the perpendicular lamellae. From the curious arrange- 
ment of these, and from their extreme minuteness and delicacy re- 
sults that particular figure which has been by different authors so aptly 
compared with the texture of the spider's web. Mr. Da Costa, speak- 
ing of this fossil, says, “ When polished, all these angular columns shew 
themselves on the surface, in a fine net-work of heptagonal, hexagonal, 
pentagonal, &c. meshes, and each mesh is adorned with a fine radiated 
star in it; and what with the beauty of the network and stars, and 
exquisite polish and fine surface it is capable of, it is as elegant a fossil 
as any of the fossil kingdom.* 
* A Natural History of Fossils, by Emanuel Mendes Da Costa, Vol. I. P. 247. 
